This invention relates to a liquid separating composition used for centrifugal separation of a liquid substance consisting of at least two components having different specific gravities and to an apparatus for applying the composition to the liquid substance to be separated.
It is widely known to the art to separate centrifugally a liquid substance consisting of at least two components having different specific gravities into component layers. For example, the whole blood collected in a test tube for the blood examination is subjected to centrifugal separation so as to isolate the blood serum and the blood plasma from the blood corpuscle for na analytical purpose. For this whole blood separation, it is known to use a liquid separating composition (or a barrier) having a specific gravity intermediate between those of the blood serum and the blood corpuscle. The liquid separating composition mentioned is filled in advance in an evacuated test tube in which the whole blood is to be collected or added to the whole blood collected in a test tube.
For example, U.S. Pat. No. 3,852,194 discloses an evacuated blood collecting tube having a gel-like liquid separating composition positioned in advance at the bottom portion. U.S. Pat. No. 3,780,935 discloses another type of device. In this case, a vessel containing a liquid separating composition and provided with a nozzle at the bottom is mounted on the opening of a test tube filled in advance with the whole blood. The assembly of the vessel and the test tube is rotated so as to enable the liquid separating composition to be injected centrifugally through the nozzle of the vessel into the whole blood collected in the test tube.
In the prior art mentioned first, the composition positioned in the bottom of the test tube is caused to rise up to the central portion of the test tube in the subsequent step of centrifugal separation of the whole blood. A major problem inherent in this technique is that collision takes place between the rising composition and the solid components of the blood, resulting in destruction of blood corpuscles to cause hemolysis. Another difficulty to be noted is that fibrin is partially included in the separated serum portion because a barrier layer consisting of the liquid separating composition is merely advanced up to the intermediate portion of the blood layers.
In the other prior art, i.e., U.S. Pat. No. 3,780,935, a rubber stopper of the tube containing the whole blood is removed first and, then, the vessel having the composition is mounted on the opening of the blood tube in preparation for the subsequent operation of centrifugal separation. In this case, the blood collected in the tube is brought into direct contact with the atmosphere because the stopper of the tube is removed first and the opening of the blood tube is not sealed air-tight by the vessel mounted thereon. It follows that the blood may possibly be contaminated by bacteria present in the atmosphere. In addition, this prior art involves troublesome blood separating operations including the removal of the rubber stopper and the mounting of the vessel containing the liquid separating composition on the opening of the blood tube. It should also be noted that the operator may possibly be infected by pathogenic organs contained in the blood because the rubber stopper touched by the operator is dotted with stains of the blood in many cases.
U.S. Pat. No. 3,780,935 mentioned above also teaches a liquid separating composition used for separation of a liquid substance, said composition being provided by a gellike mixture of a silicone fluid and a hydrophobic silicon dioxide. The composition exhibits fluidity when subjected to centrifugal operation, moves into the boundary between the phases which are to be separated, and forms a stable barrier layer sandwiched between the phases after completion of the centrifugal operation. However, this liquid separating composition is not satisfactory in that the silicone fluid reacts on the surface of the silica grain as described in detail in U.S. Pat. No. 3,977,982, resulting in decrease with time of viscosity of the composition. Accordingly, when the test tube housing the phase-separating blood is inclined for taking out the separated blood serum portion, the barrier layer formed of the liquid separating composition is mixed into the serum portion. Naturally, it gives a bad influence to the accuracy in the analysis of the separated blood serum. Further, it is undesired to preserve the test tube containing the blood whose phases have been separated by the barrier layer of a decrease viscosity.
Another difficulty to be noted is that the liquid separating composition contains a silicone fluid as a major component as mentioned previously, which brings about a lowered blood coagulation speed. Thus, a secondary treatment for promoting the blood coagulation is required in order to shorten the blood examination time. Further, such a large stress as at least about 1,000 G is required in the centrifugal separation step, presenting a cause of hemolysis. Still further, it is necessary to use an expensive centrifuge capable of high speed rotation. It is also noted that, when silicone fluid is irradiated with .gamma.-rays for the purpose of sterilization, the silicone fluid becomes too hard to centrifugal separation.